1. Field of the Invention
This invention relates to obstruction detection methods for vehicles which run together in columns under controls of automatic follow-up travel systems. Under the control of the automatic follow-up travel system, two vehicles run together in a column in an automatic follow-up manner that a following vehicle is controlled to follow up with a preceding vehicle, for example.
This application is based on Patent Application No. Hei 11-71042 and Patent Application No. Hei 11-353714 both filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Recent technologies develop automobiles being equipped with obstruction detection alarm (or warning) devices. FIG. 10 shows an example of an obstruction detection device being installed in the automobile. The obstruction detection device of FIG. 10 is mainly constructed by an ultrasonic sensor 201, a detection decision unit 202, a sound alarm device 203 and a display warning device 204. Herein, the ultrasonic sensor 201 is installed in each of a front portion and a rear portion of a vehicle. This ultrasonic sensor 201 measures distance between vehicles and detects obstructions, for example. That is, the ultrasonic sensor 201 radiates ultrasonic pulses to an obstruction. Then, the ultrasonic sensor 201 receives reflected waves corresponding to the ultrasonic pulses reflected by the obstruction. So, it is possible to detect the obstruction by receiving the reflected waves. In addition, it is possible to measure a distance to the obstruction by measuring a time for receiving the reflected waves. Thus, the ultrasonic sensor 201 produces detection signals, which are forwarded to the detection decision unit 202. Based on the detection signals, the detection decision unit 202 activates alarm (or warning) devices such as the sound alarm device 203 and the display warning device 204. That is, when the detection decision unit 202 determines that an obstruction exists in a progressing direction of the vehicle, the sound alarm device 203 generates alarm sounds while the display warning device 204 show warning signs, indications, messages or else. So, a driver of the vehicle is informed of existence of the obstruction by the alarm sounds and warning signs or else.
Automatic follow-up travel systems are proposed for saving driver""s loads in driving vehicles. Concretely speaking, unmanned vehicles are led by a manned vehicle with a driver under control of the automatic follow-up travel system. So, it is possible to actualize xe2x80x9cdriverlessxe2x80x9d conditions with respect to xe2x80x9cfollowingxe2x80x9d vehicles which travel to follow up the xe2x80x9cmannedxe2x80x9d preceding vehicle. Techniques for the automatic follow-up travel systems are proposed by a variety of papers and documents such as Japanese Patent Application, First Publication No. Hei 5-170008, for example. An example of the automatic follow-up travel system operates as follows:
A preceding vehicle transmits drive operation values such as a steering value and a throttle opening value to a following vehicle. To follow a same track in travel of the preceding vehicle, the following vehicle performs feed-forward control on a steering value and an engine control value thereof based on differences between the drive operation values of the preceding vehicle and engine outputs thereof. Thus, the following vehicle is capable of following up with the preceding vehicle.
In the aforementioned automatic follow-up travel system, a vehicle which travels independently is equipped with an obstruction detection alarm device. In that case, it is necessary to activate all ultrasonic sensors installed in front and rear portions of the vehicle in consideration of the cost of the device or in consideration of inactivation of switching operations of the sensors which are required when the vehicle changes a travel direction. Now, suppose a situation where a present vehicle adjoins two vehicles in the travel direction thereof in such a way that the present vehicle runs between them. That is, a front-side vehicle runs in front of the present vehicle while a back-side vehicle runs to follow the present vehicle. In such a situation, the present vehicle is placed under influence of ultrasonic waves which are radiated from a back portion of the front-side vehicle, and it is also placed under influence of ultrasonic waves which are radiated from a front portion of the back-side vehicle. Those ultrasonic waves interfere with each other with respect to the present vehicle. As a result, a failure may occur in the obstruction detection alarm device of the present vehicle such that the ultrasonic sensor outputs xe2x80x9cerrorxe2x80x9d sensor signals to the detection decision unit. In other words, the ultrasonic sensor installed in the front portion of the back-side vehicle makes an error in detection of an obstruction, which does not actually exist but whose existence is mistakenly detected. Or, it makes an error in detection of an obstruction, which does actually exist but whose existence is not detected. Such an error induces an error operation of the alarm device. In short, the conventional obstruction detection techniques suffer from a problem corresponding to a xe2x80x9clowxe2x80x9d accuracy in detection of obstructions.
It is an object of the invention to provide an obstruction detection method for a vehicle, which has a high accuracy in detection of obstructions and which avoids mutual interference of waves radiated from adjoining vehicles in follow-up travels.
This invention is applicable to an electric vehicles sharing system (or automatic follow-up travel system), wherein a number of (electric) vehicles are stored in ports and are used by drivers to achieve assigned objects. Herein, multiple vehicles run together in column in an automatic follow-up manner in such a way that following vehicles which are normally unmanned automatically follow up with a manned preceding vehicle. Each vehicle is equipped with ultrasonic sensors, which are arranged in a front portion and a rear portion respectively and each of which is used to detect an obstruction. Normally, each vehicle detects a travel direction thereof (i.e., a forward or backward direction) to activate only a sensor which matches with the travel direction; Thus, ultrasonic waves radiated from the ultrasonic sensors do not mutually interfere with each other among the vehicles which run together in column. So, it is possible to avoid error detection in which the ultrasonic sensor detects an obstruction which does not actually exit or error detection in which the ultrasonic sensor fails to detect an obstruction which does exit.
In addition, if a vehicle detects an obstruction being located within a deceleration decision range which is determined in advance and which lies in the travel direction by the ultrasonic sensor, it is automatically being decelerated while it also transmits a deceleration instruction to other vehicles by radio communication, so that the other vehicles are automatically being decelerated. Thus, it is possible to keep a constant distance between the vehicles which run together in column.
Further, if a vehicle detects an obstruction being located within a stop decision range which is determined in advance and which is smaller than and included in the deceleration decision range, it is automatically being stopped while it also transmits a stop instruction to other vehicles by radio communication, so that the other vehicles are automatically being stopped. Thus, it is possible to avoid an accident and collision between the vehicles or between the vehicle and obstruction.
Furthermore, if a failure occurs on a sensor of a following vehicle which is activated and is arranged in the travel direction, the following vehicle transmits failure information to its ahead vehicle which runs ahead of the following vehicle, so that the ahead vehicle automatically activates a sensor which is arranged in a direction reverse to the travel direction. Thus, even if a failure occurs on the sensor of the following vehicle in the travel direction, the ahead vehicle activates the sensor to compensate absence of detection due to the failure.